Although the prior art teaches a number of sonar or ultrasonic ranging devices, typical of which is that shown in U.S. Pat. No. 3,360,775 to Schroeder, and U.S. Pat. No. 3,922,629 to Hayakawa, there do not appear to be any prior art ultrasonic ranging devices specifically adapted for use by most drivers of passenger vehicles.
It is clear that the advantages to be obtained from such a device are many. For instance, the ranging device can be used as a warning system for a person backing a car. Oftentimes, a person may not step out of the car to look behind it before he backs up or may only take a quick glance in the rear view mirror. Children are often injured or killed by drivers backing down driveways. Most people are also familar with persons unlucky enough to strike objects, such as posts, while parking their cars. A low cost reliable ultrasonic ranging device of the type hereinafter described can solve many of these problems.
The Schroeder patent is directed to an anti-collision device for use on a catering vehicle, such as an airport catering truck. The device is adapted to be used in conjunction with a control system for automatically braking the vehicle should collision become imminent. Furtheremore, the system has circuitry which provides an audible warning of rising frequency as the vehicle approaches the obstacle, the warning frequency being inversely proportional to the distance from the object. In addition, separate transducers 47 and 47' are employed, increasing the cost of the device.
Likewise, the Hayakawa patent teaches a unit having separate sending and receiving transducers used in conjunction with a wobbler 14 to provide a fail-safe unit.
Additional examples of ultrasonic ranging devices for use in vehicles are disclosed in U.S. Pat. No. 3,806,861 to Okumura et al., which teaches a system requiring an active reflector 20 having both a receiver and a transmitter.
U.S. Pat. No. 3,842,397 to Sindle, which discloses a scheme for employing a plurality of ultrasonic transducers and receivers, all functioning simultaneously.
British patent specification No. 1,509,756 to Mukhin et al. for an ultrasonic vehicle detection device which discloses a clock pulse generator connected to control an oscillator and a switching circuit.
Thus, it is clear that what is needed is a relatively low cost system which can inform the driver through the use of a bell or other tone that the driver is within a predetermined range of an obstacle, whether the vehicle is moving or not.